This invention relates to an apparatus for noise suppression in a tubular channel, in particular a gas-carrying channel of an internal combustion engine.
Published German patent application no. DE 195 43 967 A1 describes a device for suppressing intake noise of an internal combustion engine which has a pulsating operation, in which a bypass channel is provided, running parallel to a main channel with a greater distance between a branch and an opening into the bypass channel in a segment of the tubular intake channel. The longer bypass tube should be arranged in the manner of an interference pipe, whereby the length of the bypass tube and the length of the main channel of the intake line which is parallel to it are constructed with dimensions such that noise from harmonics of an interfering noise frequency are suppressed due to interference. The known bypass tube ends at one end at an acute angle which is open in the direction of flow of the intake air and at its other end it opens into the intake tubular channel at an obtuse angle, or preferably at a right angle.
Published European patent application no. EP 1,070,903 A1 describes a device of this general type in which a curved bypass channel is provided, branching off from the tubular channel at a right angle and opening back into the tubular channel at a right angle again at the end of the segment. The interference suppressor described here forms a three-peak suppression curve at the design frequency, resulting from the interference conditions. The dip in noise suppression down to less than 10 dB between the three peaks limit the broadband usability of this noise suppressor. Suppression values of at least 20 dB are necessary in such cases. This disadvantage is avoided by using two additional λ/4 pipes, the lengths of which must be designed for these frequency ranges.
French Patent FR 602,160 describes a spiral pipe system with different spiral pitches. The acoustic transit time difference produced in this way is proposed as the interference suppressor for exhaust systems. Here again, the transit time difference L of half the wavelength or an uneven multiple of half the wavelength of the frequency range to be suppressed amounts to
  d  =      2    *    L    ⁢                  f        mid            U      where υ is the velocity of sound and d is the number of the lambda contained in 2*L because
            f      mid        U    =      λ    .  An enhancement of the noise suppression effect is to be achieved by a multiple series connection, i.e., cascade of the same component.
The devices known from the prior art require a substantial amount of space to arrange the curved bypass channels, some of which extend a great distance away from the main channel. In addition, manufacturing the bypass channels is complex. In particular in noise suppression of internal combustion engines for motor vehicles, the available space is often very limited, so the known devices are too large and are not suitable for use with automobile engines.